A disposable diaper will conventionally comprise a backsheet which is impervious to liquids, typically a PE backsheet, a topsheet which is pervious to liquids and in contact with the body part, and sandwiched in between an absorbent core. The absorbent core is usually available in a core wrap, i.e. an envelope around the absorbing material. This core wrap or envelope typically comprises a bottom layer and a top layer, where the bottom layer contacts the backsheet and the top layer contacts the topsheet. An acquisition/distribution layer can also be present, where this layer can be in the core wrap (between the absorbent itself and the top layer) or outside the core wrap (between the top layer and the topsheet). It is also possible that the bottom layer be omitted and the backsheet then plays both roles of backsheet per se and bottom layer. It is also possible that the top layer be omitted and the topsheet then plays both roles of topsheet per se and top layer.
In disposable diapers, originally wood pulp fluff was used as the sole material for absorbing liquid, in this case urine. The problem with wood pulp fluff, however, was its poor wet strength and its tendency to collapse when wet which in turn often resulted in diaper leakage.
As the advances in diaper construction progressed, high absorbency materials such as fluid absorbent polymer particles or superabsorbents (Super Absorbent Polymers—SAP—) were mixed in with the wood pulp fluff to increase the overall liquid retention capacity of the diaper's absorbent core. This in turn allowed for a reduction in the overall thickness of the diaper by removing a portion of the wood pulp fluff and supplanting it with higher and higher quantities of the superabsorbent.
The development of SAP was such that an absorbent article especially an absorbent core without fluff (Fluff Free Core) is now possible, the SAP being the sole component for absorbing the liquid.
One problem when using superabsorbent is their need to swell or expand as they absorb liquid. If the particles are too closely confined, the particles cannot freely expand, and/or the swelled particles can cause rupturing of the materials around them which in turn can allow the superabsorbent to ooze out and possibly come in contact with the wearer. On the other hand, if the SAP particles are left free, then problems during transport and especially during liquid uptake will be generated. When simply placed between two sheets in a diaper, the SAP particles can flow and tend to accumulate at one place of the diaper, leaving the other place devoid of SAP, hence without liquid-absorbing capacity. Also, once the SAP particle has absorbed water and has swollen, these can create a barrier that blocks the passage of fluids into the centre of absorbent article especially the centre of the Fluff Free Core and therefore reduces or even block the absorption capacity for further acquisition of liquids (“gel blocking”). Additionally the swollen particles can flow and accumulate at one place of the diaper, with the same drawback as mentioned before. Another drawback is the unpleasant feeling generated by the accumulation of swollen material at one place of the diaper.
SAP distribution for use in a diaper is thus an issue in diaper manufacturing, and generally speaking in any absorbing article.
Livedo has developed a technology that is disclosed in EP1609448. It is disclosed a disposable absorbent article comprising an absorbent mat between a liquid-permeable top sheet and a liquid-impermeable back sheet, wherein: the absorbent mat includes (i) a sheet-shaped water-absorbent layer that contains SAP that is fluff-free and (ii) a fiber assembly layer that contains SAP and pulp fibers in this order from a top sheet side; and where the layer (i) includes a plurality of SAP presence regions in each of which the SAP powder is wrapped and a plurality of SAP absence regions between presence regions. The SAP is placed between non-woven fabric layers. Upon liquid uptake, the SAP increases the volume of the presence regions in the range of expansion allowed by the unwoven fabrics.
Another technology has been developed by Fameccanica that is disclosed in EP1974705. It is disclosed an absorbent element comprising: a first layer of sheet material presenting an array of hollowed formations with respective so-called “mouth parts”; SAP arranged in said hollowed formations; a second layer of sheet material, applied on said first layer of sheet material covering the mouth parts of said hollowed formations. The SAP expands in the hollowed formations and the second layer of sheet material being what is called “compliant” in an area corresponding to the mouth parts of said hollowed formations, enabling the further expansion of said masses of superabsorbent material beyond said hollowed formations. The term “compliant” is supposedly used to refer to a deformable part of the layer. The SAP is thus placed in a hollow cavity and will firstly expand to fill in the cavity and secondly by expanding the “compliant” part of the top layer.
According to the sole disclosed embodiment, the hollow formations are linked with adhesives, where one of the adhesive is a water-soluble glue. Upon contact with the liquid to be absorbed, the glue dissolves and the SAP can further expand to form one unique mass in a volume that can be defined as a tube.
The above techniques still do not completely solve the problem of the movement of the SAP in the cavities or in the absorbent article, before and/or after liquid absorption and the problem of gel blocking.
Consequently, there is a need for an improved liquid-absorbing article containing SAP where the SAP is maintained in place in an efficient manner.
A further object of the present invention is an absorbent article having improved properties in respect to the passage of fluids to the centre of the absorbent article or hollow cavities respectively and/or less or no gel blocking.